This invention relates to a method of recovering or removing volatile organopolysiloxanes from fluid streams in a column containing a soil bed.
Although much has been published concerning the degradation and fate of organopolysiloxanes in the environment, as well as their activity or inactivity on wet and dry soils, no one to our knowledge has applied these learnings, and derived a practical method of separating volatile organopolysiloxanes from fluid streams such as air containing the volatile organopolysiloxanes. See for example, Environmental Toxicology and Chemistry, Volume 13, No. 7, Pages 1061-1064, (1994), Volume 13, No. 11, Pages 1753-1759, (1994), Volume 14, No. 8, Pages 1299-1305, (1995); Environmental Science & Technology, Volume 13, Pages 676-679, (1979), and Volume 29, No. 4, Pages 864-868, (1995). Such a method would be invaluable, in view of the increased use and presence of volatile organopolysiloxanes in our industrial, commercial, and consumer environments.
Accordingly, we have taken advantage of such learnings including the fact that (i) volatile organopolysiloxanes can be adsorbed on dry soil by virtue of the presence of an induced dipole caused by cations on the clay surfaces of the soil; (ii) volatile organopolysiloxanes are not adsorbed by wet soil because of their hydrophobic nature; (iii) volatile organopolysiloxanes degrade on dry soil as a function of time due to the catalytic action of the clay surfaces of the soil; and (iv) volatile organopolysiloxanes do not degrade at a significant rate on wet soil by virtue of the water present, which functions as a barrier preventing approach of the volatile organopolysiloxane to the catalytic clay surfaces in the soil.
The main degradation product of volatile organopolysiloxanes on dry soil is dimethylsilanediol (CH.sub.3).sub.2 Si(OH).sub.2. There is little or no degradation of volatile organopolysiloxanes to dimethylsilanediol on wet soil, however. Its presence, therefore, is not detrimental according to the purposes of our invention.
This is for the reason that while dimethylsilanediol is water soluble, it is immobile on dry soil, and so it can be removed along with the volatile organopolysiloxane, when a column containing dry soil is flushed with water. In addition, where the objective is to recover as much volatile organopolysiloxane as possible, then it becomes a simple matter of regenerating the soil beds in the column on a more frequent basis, before significant portions of the volatile organopolysiloxane has degraded to dimethylsilanediol. On the other hand, where the objective is to merely remove a volatile organopolysiloxane from a fluid stream, then the soil bed in the column can be regenerated on a less frequent basis, and the degradation of significant portions of the volatile organopolysiloxane to dimethylsilanediol can be tolerated.